In communication systems, various schemes for acquiring high performance gain are being studied, and their typical examples include an open-loop scheme, a closed-loop scheme, a multi-antenna scheme, and a closed-loop multi-antenna scheme.
For example, compared with the open-loop system in which only the receiver can use channel information, the closed-loop system in which both the transmitter and the receiver can use channel information can have a higher performance gain.
In addition, the use of multiple antennas can also provide greater performance gain. The multi-antenna system is roughly classified into a method for obtaining diversity gain to decrease a transmission error rate and a multiplexing method for simultaneously transmitting many symbols to increase a data rate.
Based on these methods, in order to secure higher system performance, research is being conducted on a closed-loop multi-antenna technology capable of obtaining both diversity gain and multiplexing gain by using multiple antennas for the closed-loop system in which the transmitter can acquire channel information.
The typical closed-loop multi-antenna technology includes a Singular Value Decomposition (SVD) technique and a Uniform Channel Decomposition (UCD) technique. The SVD technique decomposes all channels for multiple antennas into independent subchannels, so the independent subchannels have various Signal-to-Noise Ratios (SNRs). However, in the SVD technique, low-SNR subchannels suffer performance reduction, causing an increase in the performance imbalance of the entire system.
In order to solve the problems of the SVD technique, the UCD technique was developed. The UCD technique achieves the same subchannel SNR for each subcarrier by applying a Successive Interference Cancellation (SIC) method to the receiver. Thus, compared with the SVD technique, the UCD technique noticeably improves error performance when there is no channel coding.
On the other hand, during channel coding, the UCD technique may undergo abrupt performance reduction due to an error transfer phenomenon that inevitably occurs with the SIC method used by the receiver.